Axial Spondyloarthritis Patients Who are Obese Don’t Do as Well on TNF Blockers, Study Reports

Obese patients with axial spondyloarthritis are less likely to respond to treatment with TNF blockers than patients at a healthy weight, according to a study suggesting that weight loss could improve treatment outcomes.

Heavier patients who received Remicade (infliximab) — whose doses are based on weight — did not have poorer responses, however. This suggested that patients on other TNF blockers might be getting too low a dose.

TNF is a protein that plays a role in inflammation, so blocking it can help patients with inflammatory conditions.

The findings are particularly important because doctors know that TNF blockers cause weight gain in people with axial spondyloarthritis — an umbrella medical term that includes ankylosing spondylitis. Fat tissue is a source of inflammatory factors, which means it can contribute to a poorer treatment response.

Researchers at Zurich University Hospital in Switzerland conducted the study, titled “Impact of obesity on the response to tumor necrosis factor inhibitors in axial spondyloarthritis.” It was published in the journal Arthritis Research & Therapy.

The team evaluated treatment responses in 624 patients. Fifty-two percent had normal weight, 33 percent were overweight, and 14 percent obese, according to their body mass index, or BMI.

Patients in the highest BMI group were older, had a more active disease, and were more physically impaired when they entered the study than those at other weights.

A year after starting on TNF blockers, obese patients’ disease activity had improved slightly less than that of other patients. The disease activity of patients in the normal-weight and overweight categories improved an average of 2.4 points on a widely used scale, while obese patients’ activity improved by 2 points. The scale researchers used was the Bath Ankylosing Spondylitis Disease Activity Index.

While all three groups had similar levels of fatigue when they entered the study, obese patients had higher levels than leaner patients after treatment, researchers said.

The study’s primary goal was to determine the percentage of patients in each weight category who achieved at least a 40 percent improvement in disease activity. While 44 percent of normal-weight patients achieved the target, only 29 percent of obese patients did. Overweight patients fell into the middle, with 34 percent achieving the target.

Researchers said obese patients also improved less on a range of other outcome measures.

Since Remicade is the only TNF blocker that doctors prescribe according to weight, researchers took a closer look at outcomes of the patients taking it. They found no difference in treatment response among the three weight categories, but obese patients responded better to Remicade than other TNFs.

The findings suggested that obese patients treated with other TNF blockers might be receiving too low a dose. Researchers cautioned, however, that their poorer treatment response could also stem from their fat tissue generating inflammation. The two scenarios do not need to be mutually exclusive, they pointed out.

They called for additional studies on the topic to obtain a more definitive answer.